1. Field of the Invention
The present invention relates to an ink container that is used for a pit-stop-type ink-jet recording head and is provided with a gas liquid separator; an ink-jet recording head; and an ink-jet recording apparatus.
2. Description of the Related Art
In ink-jet recording apparatuses, as shown in FIG. 4, a recording head 101 is guided by a guide shaft 108, and horizontally scans a recording medium to perform recording. Methods widely used for supplying ink include “a head cartridge method” and “a tube supply method.”
In the head cartridge method, as shown in FIG. 4, a head cartridge 101b is mounted on a carriage 101a. The head cartridge 101b includes the recording head 101 and a main tank 104 integrated with each other. The recording head 101 is provided with nozzles for discharging ink. The main tank 104 holds ink. The carriage 101a moves along the guide shaft 108 so that the head cartridge 101b can move to perform printing.
In the tube supply method, as shown in FIG. 5, only a head cartridge 201 is mounted on a carriage 201a. A tank cartridge 201c containing ink is disposed in the main body of the recording apparatus. The recording head 201 and the tank cartridge 201c are connected via a flexible ink supply tube 201d so that ink can be supplied from the tank cartridge to the recording head 201.
In the head cartridge method, as described above, the head cartridge 101b mounted on the carriage 101a holds ink. Therefore, the weight of ink hinders the carriage 101a from moving at a high velocity. If the size of the head cartridge 101b is reduced in order to reduce the weight, the number of printable sheets is also reduced.
In the tube supply method, as described above, the recording head 201 and the tank cartridge 201c are connected via the ink supply tube 201d. Therefore, the mechanism is complex, and it is difficult to reduce the size of the ink-jet recording apparatus.
In order to solve these problems, a “pit-stop-type” ink-jet recording apparatus has been devised. In the pit stop method, only a recording head is mounted on a carriage. When the carriage is in the home position or a predetermined position, a predetermined amount of ink is supplied to the recording head on the carriage.
FIG. 6 is a perspective view showing a pit-stop-type ink-jet recording apparatus. As shown in FIG. 6, a recording head 301 is mounted on a carriage 301a. A paper feed roller 321 carries recording paper 320. The recording head 301 performs recording on the paper 320. The carriage 301a is guided by a guide shaft 308. A main tank 304 is disposed at a home position 323. Ink is supplied from the main tank 304 to a sub-tank 303 of the recording head 301. The main tank 304 is provided with a joint 310 to be connected to an ink inlet 311 of the sub-tank 303. A covering cap 306 seals and protects an ink-jet recording element. An ink suction cap 305 sucks ink from nozzles of the ink-jet recording element. An air suction cap 322 sucks air from a vent 315 of the sub-tank 303. The ink suction cap 305 and the air suction cap 322 communicate with a negative-pressure generator 307.
The pit stop operation in this ink-jet recording apparatus will be described. When recording is not performed, the recording head 301 is on standby in the home position 323 where the recording head 301 can be connected with the ink suction cap 305, the air suction cap 322, the covering cap 306, and the main tank 304. When the main body of the recording apparatus receives a printing signal, the covering cap 306 seals the discharging ports of the ink-jet recording element, and the joint 310 of the main tank 304 is connected to the ink inlet 311 of the sub-tank 303. Next, the air suction cap 322 is connected to the vent 315 of the sub-tank 303. The negative-pressure generator 307 operates to reduce the pressure inside the sub-tank 303. In this way, ink is supplied from the main tank 304 to the sub-tank 303.
Next, a recovering operation is carried out in order to clear the nozzles clogged with thickened ink and to recover a good discharging performance. In this recovering operation, the vent 315 and the ink inlet 311 of the sub-tank 303 are disconnected from the air suction cap 322 and the joint 310, respectively. Next, the ink suction cap 305 is connected to the ink-jet recording element. The negative-pressure generator 307 operates to suck the ink in the nozzles. After the suction of ink, the ink adhering to the discharging surface of the recording head 301 is wiped. Next, a preliminary discharge is performed in order to remove the mixed ink that is forced to enter the nozzles by wiping. Next, recording to the recording paper 320 is started.
As described above, in the pit stop method, only the ink-jet recording element and the sub-tank 303 are mounted on the carriage 301a. Since the load of the carriage 301a is light, the ink-jet recording head 301 can scan at comparatively high velocity. In addition, in this pit stop method, ink is supplied from the main tank 304 in the home position 323. Therefore, the number of printable sheets can be increased. Moreover, unlike the tube supply method, it is unnecessary to connect the carriage 301a and the main tank 304 with an ink supply tube. Therefore, the structure of the ink-jet recording apparatus is more simple.
Japanese Patent Laid-Open No. 08-112913 discloses an ink supply mechanism for a pit-stop-type ink-jet recording apparatus. In this ink supply mechanism, at the pit stop, a sensor detects the amount of ink that can be supplied to the sub-tank, and an ink supply system is controlled accordingly. However, this mechanism is very complex and delicate, and therefore the cost of manufacturing is high.
In order to solve this problem, a pit-stop-type ink-jet recording head whose sub-tank is provided with a gas liquid separator has been proposed. FIG. 7A is a sectional view showing a pit-stop-type ink-jet recording head provided with a gas liquid separator. FIG. 7B is a sectional view taken along line B-B of FIG. 7A.
This ink-jet recording head is mounted on the ink-jet recording apparatus shown in FIG. 6. As shown in FIGS. 7A and 7B, an ink chamber of a sub-tank 403 communicates with an ink inlet 411 of an ink inlet pipe 412. Ink absorbers 437 are disposed in the ink chamber. The ink absorbers 437 absorb and hold the ink coming in through the ink inlet 411. A gas liquid separator 433 is fixed to the container body 435, and disposed on the boundary between an exhaust chamber 436 and the ink chamber. The gas liquid separator 433 allows gas to pass through but blocks liquid such as ink. A porous film with a thickness of tens of micrometers formed of, for example, polytetrafluoroethylene (PTFE) is used as the gas liquid separator 433.
As shown in FIG. 7B, the ink chamber is divided into three sections. The gas liquid separator 433 is welded on the inner rib of the container body 435 so as to separate the three sections from the exhaust chamber 436. In addition, an exhaust chamber cover 434 is welded on the edge at the top of the container body 435 so as to cover the exhaust chamber 436. The exhaust chamber cover 434 is formed of polysulfone resin, which is the same material as that of the container body 435. The exhaust chamber 436 is shared by the three sections of the ink chamber.
The ink supply operation in the above ink-jet recording head will be described. When the main body of the recording apparatus receives a printing signal, a covering cap 406 seals the discharging ports of the ink-jet recording element 438, and a joint 410 of a main tank (not shown) is connected to the ink inlet 411 of the sub-tank 403. Next, an air suction cap 422 is connected to a vent 415 of the sub-tank 403. A negative-pressure generator operates so as to exhaust the air from the ink chamber through the gas liquid separator 433 and the vent 415.
As a result, the pressure in the sub-tank 403 is reduced. Ink is supplied to the ink chamber through the joint 410 and the ink inlet 411 so as to refill the ink chamber. Just after this ink supply, in order to prevent defective discharge of ink, the recovering operation, the wiping, and the preliminary discharge are performed. Next, recording to the recording medium is started.
When the amount of air sucked by the negative-pressure generator is larger than or equal to the inner volume of the sub-tank 403, the air is exhausted from the ink chamber through the gas liquid separator 433 regardless of the amount of ink remaining in the ink chamber, and the ink chamber is refilled with the ink supplied from the main tank. As described above, the negative-pressure generator only has to suck at least a certain amount of air in order to refill the ink chamber. Therefore, it is unnecessary to control the air suction. When the amount of air that the negative-pressure generator can suck is sufficiently large, this ink supply method can easily be feasible in principle.
As described above, generally, the container body 435 is formed of a resin material with an injection molding machine. Since the exhaust chamber cover 434 is joined to the container body 435 by heat welding or ultrasonic welding, the exhaust chamber cover 434 is formed of the same resin material as that of the container body 435, and thin.
Therefore, the heat capacity of the exhaust chamber cover 434 is small in comparison with that of the container body 435. In addition, in order to minimize the size of the ink-jet recording head, the distance between the gas liquid separator 433 and the exhaust chamber cover 434 is very small. On the other hand, the volume of the ink chamber is large in comparison with that of the exhaust chamber 436. Therefore, after completion of printing, some ink remains in the ink chamber. The specific heat of ink is greater than that of air.
Therefore, the heat capacity on the exhaust chamber side of the gas liquid separator 433 is very small in comparison with that on the ink chamber side. Therefore, in the ink-jet recording head, when the environment temperature changes, the difference in rate of temperature change between both sides of the gas liquid separator 433 is very large.
Consequently, if the ink-jet recording apparatus is shifted from a room temperature environment to a cool temperature environment, for example, from 25° C. to −20° C., dew condensation occurs on the surface and in the pores of the gas liquid separator 433. In addition, if the ink-jet recording apparatus is returned to a room temperature environment, and then the pit-stop-type ink supply is performed, the ink in the ink chamber leaks through the gas liquid separator 433 into the exhaust chamber 436.
In the ink-jet recording head shown in FIGS. 7A and 7B, the exhaust chamber cover 434 is formed of polysulfone resin, 2 mm in thickness, and 9 cm2 in area. The distance between the exhaust chamber cover 434 and the gas liquid separator 433 is 1 mm. The full capacity of each of the three sections of the ink chamber is about 0.5 cc, and each section contains about 0.3 cc of ink.
When the specific heat of polysulfone resin is 1.3 J/g·K, the specific heat of ink is 4.1 J/g·K, and the specific heat of air is 1 J/g·K, the heat capacity on the exhaust chamber side of the gas liquid separator 433 is approximately 2.8 J·K, and the heat capacity on the ink chamber side is approximately 15.1 J·K. Therefore, the heat capacity on the exhaust chamber side is about one-fifth of that on the ink chamber side.
FIG. 8 shows the temperature change on the exhaust chamber side of the gas liquid separator 433 and the temperature change on the ink chamber side of the gas liquid separator 433 when the ink-jet recording head is shifted from a room temperature environment to a cool temperature environment of −20° C. In FIG. 8, the solid line L3 shows the temperature change on the exhaust chamber side of the gas liquid separator 433, and the dashed line L4 shows the temperature change on the ink chamber side of the gas liquid separator 433.
Since the heat capacity on the exhaust chamber side of the gas liquid separator 433 is smaller than that on the ink chamber side, the rate of temperature change on the exhaust chamber side is faster than that on the ink chamber side. Therefore, as shown in FIG. 8, when the temperature on the exhaust chamber side (L3) changes from room temperature to 0° C., it is about 5° C. lower than the temperature on the ink chamber side (L4).
FIGS. 9A to 9C are schematic sectional views showing the state on the surface and in the pores of the gas liquid separator 433. How ink leaks through the gas liquid separator 433 will be described. In FIGS. 9A to 9C, for the sake of convenience, the pores in the gas liquid separator 433 are shown schematically. However, as described above, the real gas liquid separator 433 is a thin film with a thickness of tens of micrometers. Since the heat capacity of the gas liquid separator 433 is small, the rate of temperature change of the gas liquid separator 433 is close to that on the exhaust chamber side of the gas liquid separator 433.
On the other hand, the ink chamber is filled with a gas whose temperature is higher than that of the gas liquid separator 433. In addition, since ink remains in it, it contains a large amount of water vapor. Therefore, as shown in FIG. 9A, the air in the ink chamber is cooled on the ink-chamber-side surface and in the pores of the gas liquid separator 433, and dew condensation 414 occurs on the ink-chamber-side surface and in the pores of the gas liquid separator 433. When the temperature becomes 0° C. or less, the dew condensation 414 and ink 413 freeze.
When the ink-jet recording head is returned to a room temperature environment, the dew condensation 414 and ink 413 melt. As shown in FIG. 9B, since water 414 exists on the ink-chamber-side surface and in the pores of the gas liquid separator 433, ink 413 adheres to the ink-chamber-side surface of the gas liquid separator 433. Therefore, the meniscus force of melted ink 413 is lost, and ink 413 enters the pores. In this way, ink passages are formed.
If the pit-stop-type ink supply operation is repeated under such condition, as shown in FIG. 9C, ink 413 leaks gradually through the ink passages into the exhaust chamber 436. If a large amount of ink 413 leaks into the exhaust chamber 436, and the exhaust-chamber-side surface of the gas liquid separator 433 is covered by ink 413, the permeability of the gas liquid separator 433 deteriorates significantly. Therefore, it can become difficult to normally supply the ink-jet recording element with ink 413.
In addition, if the ink 413 leaks from the vent (not shown), the insides of the ink-jet recording apparatus can be soiled with ink, and when recording is performed, the recording paper can be soiled with ink. The above-described phenomenon is not limited to the case where the ink-jet recording head is shifted from a room temperature environment to a cool temperature environment below 0° C. As long as dew condensation occurs, the phenomenon occurs in any case, for example, in the case where the ink-jet recording head is shifted from a high temperature and humid environment of 60° C. and 90% to a room temperature environment.